Impact of Tumor Size on Cancer Specific Mortality After Local Tumor Ablation in T1a Renal Cell Carcinoma - Beyond the Abstract

NCCN guidelines recommend ablation for renal masses up to 30 mm since above this threshold the risk of recurrence significantly increases. We investigated whether tumor size above 30 mm may also predispose to worse cancer-specific mortality.

Within the SEER database, we identified a large cohort of 3,946 T1a RCC patients treated with ablation between 2004 and 2015. Among these patients, approximately 25% (972) harbored tumor size above 30 mm. Five-year cancer-specific mortality rates were compared according to tumor size (tumor size ≤30 mm vs >30 mm). We relied on propensity score matching to maximally reduce potential baseline differences between the two groups and we also relied on competing risks regression models to account for other-cause mortality.

Our analyses showed that tumor size >30mm was associated with significantly higher five-year cancer-specific mortality (4.7 vs 2.0%, p<0.001) and five-year other-cause mortality (13.7 vs. 7.9%, p<0.001). These rates were confirmed even after propensity score matching. It is of note that patients with tumor size >30mm experienced almost double rates of other-cause mortality, relative to those with tumor size up to 30mm. This finding indicates that ablation tumor size >30mm patients is at least partially reserved for patients at higher risk of other-cause mortality. Additionally, multivariable competing risks regression models showed a 2.8-fold increase of cancer-specific mortality, even after other-cause mortality adjustment, for tumor size >30mm. We performed a meta-analysis of previous institutional studies that compared ablation according to tumor size, showing an almost 5-fold increase of recurrence for tumor size >30mm. Even though recurrence could not be assessed within the SEER database, our findings are highly consistent with the analyses on an earlier survival endpoint, namely recurrence. Finally, as exploratory analyses, we compared cryoablation and thermal ablation in both tumor size groups. We demonstrated significantly higher five-year cancer-specific mortality when thermal ablation is used for tumor size >30mm, compared to cryosurgery.

The findings of our study should be considered in clinical decision making and at informed consent when ablation is performed for renal masses above 30mm. Specifically, we validated the NCCN recommendation of the use of ablation in patients with tumor size up to 30 mm. Patients treated for tumor size >30mm were generally older and at higher risk of other-cause mortality. These characteristics may justify the use of ablation above the recommended tumor size threshold. Nonetheless, five-year cancer specific mortality, as well as recurrence, are significantly higher. Further studies are needed to ascertain whether the cryoablation techniques may improve survival outcomes above the threshold of 30mm. 

Written by: Carlotta Palumbo, MD, Department of Urology, Università degli Studi di Brescia and Pierre I. Karakiewicz, MD, Division of Urological Surgery, Université de Montréal

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